Spring hinge



FIG. 1 is a side symmetrical left and right view of a spring hinge showing our new design;

FIG. 2 is a rear end view thereof;

FIG. 3 is a front end view thereof;

FIG. 4 is a bottom view thereof; and,

FIG. 5 is a top view thereof. 

The ornamental design for a spring hinge, as shown and described. 